add tag-push action to advanced usage section

README.md

@@ -31,6 +31,7 @@ ___
   * [Secrets](docs/advanced/secrets.md)
   * [Isolated builders](docs/advanced/isolated-builders.md)
   * [Push to multi-registries](docs/advanced/push-multi-registries.md)
+  * [Copy between registries](docs/advanced/copy-between-registries.md)  
   * [Cache](docs/advanced/cache.md)
     * [Registry cache](docs/advanced/cache.md#registry-cache)
     * [GitHub cache](docs/advanced/cache.md#github-cache)
@@ -166,6 +167,7 @@ jobs:
 * [Secrets](docs/advanced/secrets.md)
 * [Isolated builders](docs/advanced/isolated-builders.md)
 * [Push to multi-registries](docs/advanced/push-multi-registries.md)
+* [Copy between registries](docs/advanced/copy-between-registries.md)
 * [Cache](docs/advanced/cache.md)
   * [Registry cache](docs/advanced/cache.md#registry-cache)
   * [GitHub cache](docs/advanced/cache.md#github-cache)

docs/advanced/copy-between-registries.md

@@ -0,0 +1,73 @@
+# Copy images between registries
+
+Multi-platform images built using buildx can be copied from one registry to another without
+changing the image SHA using the [tag-push-action](https://github.com/akhilerm/tag-push-action).
+
+The following workflow will first push the image to dockerhub, run some tests using the images
+and then push to quay and ghcr
+
+```yaml
+name: ci
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - 
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - # quay and ghcr logins for pushing image after testing
+        name: Login to Quay Registry
+        uses: docker/login-action@v1 
+        with:
+          registry: quay.io
+          username: ${{ secrets.QUAY_USERNAME }}
+          password: ${{ secrets.QUAY_TOKEN }}
+      -
+        name: Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      -
+        name: Login to DockerHub
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: |
+            user/app:latest
+            user/app:1.0.0
+      - # run tests using image from docker hub
+        name: Run Tests
+        run: make tests
+      - # copy multiplatform image from dockerhub to quay and ghcr
+        name: Push Image to multiple registries
+        uses: akhilerm/tag-push-action@v1.0.0
+        with:
+          src: docker.io/user/app:1.0.0
+          dst: |
+            quay.io/user/app:latest
+            quay.io/user/app:1.0.0
+            ghcr.io/user/app:latest
+            ghcr.io/user/app:1.0.0
+```